10-year old Deedee has a horrible, horrible older brother Matthias. Matthias and his friend Peter cannot resist testing and annoying her and they are constantly in her way. One day they dare her to a race on the military assault course, a course that is strictly forbidden for them. At the assault course the boys take their pestering too far and Deedee swears she will get even with them. With the help of her old neighbor Uncle Ton and his border collie Teddie, she sets out to free everyone from Matthias’ harassments. Will she succeed in getting her brother to tone down? And who are Vrassos, Aikja and Kreis? Are they on her side or will they also turn against her?